A 4mm shaft and a housing bored to 9mm. No room to go larger in either direction. The 684 ZZ is the bearing for designs that have already shrunk every other component to its limit. At 9mm OD, it holds the smallest outer diameter in Yuanhe’s catalog. The ZZ metal shields add effectively zero drag, so the bearing reaches 57,000 RPM, a speed few bearings at this scale can sustain.
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684 bearing: double metal shielded, pre-lubricated miniature deep groove ball bearing. 4mm bore, 9mm OD, 4mm width. ABEC-3 precision, 57,000 RPM max speed with ZZ shields.
Double metal shielded, pre-lubricated miniature bearing for ultra-compact high-speed applications. 4mm bore, 9mm OD, 4mm width. ABEC-3 precision, 57,000 RPM max speed.
| Model | 684 ZZ |
| Type | Shielded |
| Bore Dia (d) | 4 mm |
| Outside Dia (D) | 9 mm |
| Width (B) | 4 mm |
| ABEC Tolerance | 3 |
| Dynamic Load Capacity (kN) | 0.715kN |
| Static Load Capacity (kN) | 0.224kN |
| Max RPM | 57,000RPM |
| Temp Range | -40~120℃ |
| Material | Steel |
| Shield Material | SPCC Mild Steel |
| Lubrication | Grease |
Bore x OD x Width
4 x 9 x 4 mm
Dynamic Load Cr
0.54 kN
Static Load Cor
0.18 kN
Max Speed
53,000 RPM
Sealing
Open / ZZ / 2RS
Precision
ABEC-1 / ABEC-3
The 684 ZZ bearing uses SPCC steel shields on both sides with a non-contact design. Each shield disc presses into a retaining groove in the outer ring, leaving a narrow radial gap between the shield bore and the inner ring shoulder. There is no rubbing contact, so the shields add zero drag. At 57,000 RPM on a 4mm bore, this matters: even a light-contact rubber seal would consume a measurable share of the bearing’s torque budget.
The gap under each ZZ shield blocks coarse dust, fibers, and debris roughly 50 microns and larger. It does not stop moisture, fine dust, or chemical vapor. Think of ZZ shields as a guard rather than a seal. For environments with water spray or sub-50-micron particulate, the 684 2RS bearing variant with contact rubber seals is the alternative, at roughly 20 percent lower top speed.
Each bearing ships pre-greased with mineral-oil-based lubricant rated for the full temperature range. The grease stays in place during operation because there is no contact seal wiping it away. In clean enclosures, this can extend relubrication intervals compared to sealed equivalents. For applications pushing past 70,000 RPM, Yuanhe offers low-viscosity synthetic oil options with oil-mist delivery.
The 684 ZZ bearing is the smallest in Yuanhe’s miniature 68x series. The 685 bearing (5x11x5mm) adds 1mm of bore and 2mm of OD, more than tripling the dynamic load capacity. The 686 bearing (6x13x5mm) pushes further to 1.08 kN. Every millimeter added to OD buys a disproportionately large gain in load rating because both ball diameter and raceway curvature scale together.
For the same 4mm bore with higher load requirements, the 604 bearing (4x12x4mm) from the 60x series offers a wider OD at 12mm with a larger ball complement. The trade-off is 3mm of housing diameter. When 9mm OD is the absolute design limit, the 684 ZZ bearing is the only option in the catalog.
ABEC-3 is the standard precision grade. ABEC-1 is available for cost-driven applications where runout tolerance is relaxed. ABEC-5 is offered for gyroscope rotors, optical choppers, and instrument spindles requiring sub-5-micron runout control.
Standard 684 ZZ bearings ship in GCr15 chrome steel with CN radial clearance and SPCC metal shields. Yuanhe offers the following modifications for volume OEM orders:
440C Stainless Steel
Rings and balls in 440C martensitic stainless. For surgical power tools and lab equipment exposed to autoclave sterilization and saline solutions.
C2 Reduced Clearance
For micro-positioning stages and optical alignment mechanisms where any perceptible shaft play degrades instrument precision.
Synthetic Oil Lubrication
Low-viscosity ISO VG 10 to 22 synthetic oil for applications above 70,000 RPM. Compatible with oil-mist and jet-lubrication delivery systems.
PEEK or Phenolic Cage
For instrument bearings above roughly 80,000 RPM where steel cage inertia and vibration become the limiting factors.
Standard lead time is 7 to 14 days for catalog configurations. Custom material or clearance specifications add 5 to 10 days. MOQ starts at 100 pieces for standard configs and 500 pieces for non-catalog builds. Send a drawing or target specification for a formal quotation.
Miniature DC coreless motors, dental drill air turbines, gyroscope gimbal bearings, optical chopper wheels, micro cooling fans for wearable electronics, precision potentiometer shafts, model aircraft control surface hinges, endoscopic instrument drives, laboratory micro-centrifuge rotors, fiber optic alignment stages, watchmaker lathe spindles.
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